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The causes of irregular and heavy periods

This article has been written by one of the UK's leading Gynaecologists for any woman concerned about her irregular or heavy periods. Find out what might be causing irregular or heavy periods and find out what tests will be used for a diagnosis.

What are the causes of irregular and heavy periods?

Irregularity and heaviness of periods may be due to a number of causes including fibroids (non-cancerous growths) of the womb, polyps (abnormal growth of tissue from the lining of the womb), thickening of the lining of the womb (hyperplasia), adenomyosis of the womb (non-cancerous condition of the womb that often mimics the symptoms of fibroids), bleeding or clotting problems, blood thinning medication, hormonal imbalance or, very rarely, cancer of the womb or of the neck of the womb (cervix). I will discuss these conditions below.

What are fibroids?

Fibroids (also known in medical terms as myomas or leiomyomas) are benign (non-cancerous) lumps of smooth muscle which grow from the wall of the womb. They are very common and on average are found in 20-30% of women during their childbearing years. They are more frequently found in older women and by the time a woman reaches the age of the menopause, her risk of having a fibroid is around 70-80%. However, the majority of fibroids are harmless and often do not cause any symptoms.

Fibroids are more likely to cause heavy and irregular periods when they are located inside the cavity of the womb or protruding into it. These fibroids are called submucosal fibroids and even when they are small they can cause heavy period bleeding, bleeding in between periods or completely irregular, erratic cycles. These symptoms may also be caused when the fibroids are very large, or when there are many fibroids causing significant enlargement of the womb. These fibroids may be completely located in the muscle layer of the womb (intramural fibroids) or grow outwards from the surface of the womb (subserosal fibroids).

What are polyps?

Polyps are ‘skin-tags’ that grow from the lining or neck of the womb. They are benign growths, which means that they are harmless, and they are extremely common. Large polyps may cause heavy and/or irregular periods. Smaller polyps may be less likely to cause heavy periods but they may still cause bleeding in between periods. Polyps of the neck of the womb may cause bleeding after sexual intercourse.

What is abnormal thickening of the lining of the womb?

The medical term for abnormal thickening of the lining of the womb (the endometrium) is hyperplasia. The lining of the womb is normally very thin immediately after a period and it gradually thickens towards the middle of the cycle under the influence of the hormoneoestrogen. After the ovulation (release of the egg), the thickening comes to an end, and this is controlled by the hormone progesterone. The lining of the womb then sheds as a period. Abnormal thickening of the lining of the womb (endometrial hyperplasia) usually occurs when there is a hormonal imbalance that results either in dominance of the oestrogen hormone or in the absence of the progesterone hormone. Typical examples of these conditions include women who do not ovulate due to ‘polycystic ovary syndrome’ and overweight/obese women who produce excessive oestrogen hormone in their adipose (fat) tissue. In these situations, the lining of the womb is stimulated by the oestrogen hormone constantly, resulting in the abnormal thickening, without the protection of the progesterone hormone. Thickened lining may shed from time to time, causing an irregular pattern of bleeding which tends to be quite heavy.

In addition, certain types of thickening can progress to cause abnormal changes of some cells (this is called atypia) and this carries a risk of developing into cancer of the lining of the womb (endometrial cancer) in some women. In these circumstances abnormal changes to cells is considered a pre-cancerous condition.

What is adenomyosis?

Adenomyosis is a condition where tissue from the lining of the womb is found in the muscle layer of the womb. It is similar to endometriosis but in endometriosis the tissue from the lining of the womb is located outside the womb. Adenomyosis causes bleeding in the muscle layer of the womb every month when a woman has a period. This bleeding results in thickening of the wall of the womb, with small pools (cysts) of blood collection in the muscle layer. As a result, women with adenomyosis have enlarged wombs and may experience heavy and painful periods. Adenomyosis and endometriosis may sometimes be found together.

Heavy periods caused by blood-clotting disorders

Some women may have excessive blood loss during their periods due to problems in their blood-clotting system. These problems are usually due to genetic disorders and the women who have them also usually have a history of bruising very easily and prolonged bleeding from minor cuts. (One example of this sort of condition is von Willebrand Disease (vWD). Women suffering from these problems tend to have heavy periods starting in their teenage years.

Heavy periods caused by blood thinning medication

Some women may have heavy periods because they might be using blood thinning injections (such as heparin) or tablets (such as warfarin). These drugs are used for prevention of thrombosis in certain situations, for example in women with artificial heart valves, with history of thrombosis.

Heavy periods caused by hormonal disorders

Women who do not ovulate (release an egg) regularly tend to have irregular periods. Typically this occurs during the teenage years, the pre-menopausal years (years leading up to the menopause) and in women with polycystic ovary syndrome. In these situations, lack of ovulation leads to irregular shedding of the lining of the womb and sometimes thickening of the lining (see hyperplasia section above) and this causes irregular and sometimes heavy periods.

Cancer of the womb/neck of the womb

Cancers of the womb and the neck of the womb are rare in childbearing age women who have regular smear tests. Cancer of the womb is more commonly seen in women after the menopause, but can occasionally occur in women with severe polycystic ovary syndrome and obesity.